Microbial activation of layer silicates

ABSTRACT

A process for the microbial activation of layer silicates.

The invention pertains to a process for the activation of layersilicates with use being made of microorganisms.

U.S. Pat. No. 1,492,184 describes the activation of raw clay withmaximally 10% by weight of concentrated acid. It is preferable that apre-dried and ground raw clay be impregnated in this regard.Montmorillonite, bauxite, willonite, pyrophyllite, kaolinite andfuller's earth are designated as examples of “clays”.

U.S. Pat. No. 1,752,721 describes a process for the treatment of “earthymaterials” in order to increase their adsorption properties;accordingly, a clay material is mixed with solid oxalic acid and then itis heated, in the absence of added water, in order to bring about areaction between the oxalic acid and the clay mineral. The clay mineralis treated with approximately 1 to 5% of oxalic acid in this connection.

DE-C-304706 describes a process for increasing the decolorizing power offuller's earth. In this process, the raw fuller's earth is stirred withthe acid to give a doughy mass, and then it is dried.

A process for the treatment of clay is known from U.S. Pat. No.4,847,226 in which the clay is extruded, ground and then added to anaqueous solution of an acid in order to produce a suspension; thesuspension is heated, and then the acid-treated clay is separated,washed, filtered off and dried. The intended purpose of the treatment isto improve the ability of the clay to filter out impurities fromliquids. In particular, oil-soluble dyes are removed from oils.

The objective of the invention is to provide a process for theactivation of layer silicates without the addition of corrosive acidsthat can cause intense burns and that endanger natural water systems.whereby this process is superior to the prior art from the standpointsof operational safety and environmental protection and also from aneconomic point of view.

Surprisingly, it has now been found that the activation of layersilicates can take place via the use of microorganisms without anyaddition of an acid or, as the case may be, a solution of an acid.

The use of acid-producing microorganisms for leaching out residues fromlow grade copper ores is already known in the prior art. In addition,the growth of such microorganisms on ores, such as pyrites, is exploitedin order to assist flotation. A review of these and further applicationsof the treatment and processing of ores and for metal recovery is to befound in the publication by C. L. Brierley: Bacteria as aids in mining;Spetrum der Wissenschaft: Industrielle Mikrobiologie, 60 (1989).

The bacterial oxidation of elemental sulfur is exploited in agriculturein order to make sulfate available to plants and to make phosphate andmicro-nutrient substances available as well.

The use of microorganisms for the activation of layer silicates is notknown in the prior art.

The term “activation” is understood to mean a process for increasing thedecolorizing activity of the layer silicate.

The activated layer silicates in accordance with the invention can beused, in particular, as fuller's earth materials for the treatment ofoils, fats or waxes.

Glyceride oils, waxes and fats and mineral oils are passed through oneor more adsorptive treatment stages using inorganic adsorbents duringtheir refining. The oil or fat that is to be treated is thereby broughtinto contact with an inorganic adsorbent at an elevated temperature. Theadsorbent filters from the oil substances that are disadvantageous insubsequent processes or for storage, such as e.g. pigments,phospholipids, materials that produce turbidity, metals, free fattyacids, oxidized compounds, etc. In order to do this, the adsorbentrequires adsorptive properties, in order to permit the removal ofphospholipids or chlorophyll materials, and catalytic properties fordegrading dyes or peroxide compounds that are contained in the oil.

Because of their advantageous properties, especially their high specificsurface area, sorption capacity and ion exchange capacity, the activatedlayer silicates that are prepared in accordance with the invention canalso find use in other sectors.

The layer silicates that are listed in Ullmaiin's Encyklopädie dertechnischen Chemie [“Encyclopedia of industrial Chemistry”], Volume 21,pages 370–375 (1982) are included among the layer silicates that areusable in the process in accordance with the invention. In particular,use can be made of natural and synthetic clay minerals that are capableof being activated, such as the smectites—including montmorillonite,beidellite, nontronite, wolchonskoite, stevensite, hectorite,swinefordite, saponite and sauconite—along with vermiculites, illites,mixed layer minerals, palygorskite (attapulgite) and sepiolite. Thelatter two materials are also designated as hormites. The clay mineralscan be present in their H form, their alkali metal form or theiralkaline earth form.

In accordance with a preferred form of embodiment in accordance with theinvention, the layer silicate is a three layer silicate, e.g. anaturally occurring smectitic clay, especially a bentonite clay or apalygorskite clay or mixtures thereof.

Palygorskite clays comprise attapulgite clays that are also known asattalpulgus clays, or Georgia fuller's earths. As a rule, these claysconsist primarily of the mineral attapulgite, i.e. a crystalline,hydrated magnesium aluminum silicate, but they can also containconsiderable quantities of other minerals, such as e.g. bentonite(montmorillonite), calcium carbonate, quartz and feldspar and, in manycases, sepiolite. The preferred clays contain at least 10% by weight,and up to 90% by weight, of attapulgite and, preferably, up to 20 to 60%by weight thereof.

Non-calcined, naturally occurring mixtures of palygorskite clay andcalcium bentonite clay are especially preferred. Such natural mixturescan contain pyrites that can serve as a substrate for sulfur-oxidizingbacteria and iron-oxidizing bacteria such as Thiobacillus ferrooxidans.

An attapulgite bentonite mixture of clays is used in accordance with anespecially preferred form of embodiment.

The microorganisms that are used for activation in accordance with theinvention are bacteria, archaebacteria or fungi e.g. of the Aspergillus,Acidianus, Acidimicrobiumn, Acidiphilium, Acidobacterium, Acidocella,Alicyclobacillus, Leptospirillium, Metallosphaera, Picrophylus, Sarcina,Stygiolobus, Sulfobacillus, Sulfolobus, Thermoplasma, Thiobacillus andThiomonas strains. In addition to the acid-producing bacteria that arepreferred here—especially the so-called sulfuric acid bacteria—use canalso be made of nitric acid bacteria and acetic acid bacteria as well asmicroorganisms that produce oxalic acid, citric acid, gluconic acid orother organic acids.

The use of bacteria that oxidize pyrites is especially advantageous whenthe layer silicate that is used already contains pyrites, so that thisnutrient substance for the bacteria does not have to be added. Inaddition, it has been found that some naturally occurringbentonite/attapulgite clay mixtures already naturally containThiobacillus ferrooxidans and Thiobacillus thiooxidans in smallquantities, and these can be induced to activate the layer silicate.

The last two types of bacteria that were designated are stronglychemolithoautotrophic, i.e. their growth cannot be stimulated byproviding organic materials, such as nutrient substances or vitamins.Both belong to the group of acidophilic bacteria and they prefer pHvalues around 2 and temperatures of around 30° C.

Use can be made of both natural type strains of the microorganisms andalso strains that have been cultivated in the laboratory (e.g.Thiobacillus thiooxidans DSMZ-11478; Aspergillus niger DSMZ-823; see theDSMZ catalog, 1998). Prior cultivation of the microorganisms offers theadvantage that adaptation can be carried out using the conditions thathave been selected for the activation of the layer silicate. Inaddition, the microorganisms can be selected conventionally in terms ofadvantageous properties (e.g. rapid growth under the conditions thathave been selected for activation).

In the case of using aerobic microorganisms (such as, for example, T.thiooxidans, T. ferrooxidans and A. niger), an adequate supply of oxygenhas to be ensured during activation of the layer silicate. This can beensured, for example, by regular mixing in with the layer silicate(every 1 to 7 days) and avoiding excessive compaction. The process ofmixing in also encourages uniform distribution, more rapidmultiplication and higher metabolic efficiency of the microorganisms; asa result, activation of the layer silicate can be influenced in apositive manner.

It has been found that some naturally occurring bentonite/attapulgiteclay mixtures already contain low concentrations of T. thiooxidansand T.ferrooxidans. As a rule, however, it is preferable to add the bacteriato the layer silicate. This can take place, for example, by spraying thelayer silicate with a concentrated bacterial culture or by mixing withan inoculant material that has a high concentration of bacteria. Thefollowing are suitable, in particular, as the inoculant material: asample of the layer silicate, which is to be activated or which, as thecase may be, has already been bacterially activated, or a bacterialsubstrate (such as sulfur or pyrites) with a concentration of 10²–10¹⁰bacteria/g of inoculant material, or mixtures thereof.

In accordance with one embodiment in accordance with the invention, anutrient substrate in the form of sulfur, pyrites and/or a nutrient saltsolution is added to the layer silicate for better growth of themicroorganisms. The addition of sulfur is required, in particular, whenuse is to be made of purely sulfur-oxidizing microorganisms and thelayer silicate naturally contains no source of energy (sulfur source oriron source, respectively) that is capable of being utilized by themicroorganism in question.

The treatment of the layer silicate with the microorganisms is carriedout under conditions that are favorable for the microorganism (ormicroorganisms) in question. The technical expert will be familiar withthese conditions on the basis of the relevant prior art.

Thus, for example, one has to ensure that the microorganisms receive anadequate supply of nutrient substances (e.g. N, K, Ca, Mg, P), vitamins,metabolic substrates, gases (e.g. oxygen, carbon dioxide). If thematerial that is to be activated naturally contains too little of thesubstances that are required by the microorganisms that are used in eachcase, then these can be added to the material.

In the case of using T. ferrooxidans and T. thiooxidans, nutrient saltsand/or energy-supplying substrates (e.g. sulfur, pyrites) can be addedto the material that is to be activated. Since the designated bacteriaare, of necessity, chemolithoautotrophic organisms, these cannot bestimulated via an addition of organic substrates, vitamins or nutrientsubstances. In some cases, an excessive supply of nutrient salts, inparticular, have a negative influence on the activity of themicroorganisms.

In the case of utilizing Aspergillus niger, glucose, sucrose or molassescan be added to the substrate.

An adequate water content of the medium or, as the case may be, thelayer silicate, and maintenance of a suitable temperature have to beborne in mind as well. Thus, for example, temperatures of approximately20 to approximately 35° C. and, especially, approximately 30° C., and awater content of more than approximately 15% by weight and, inparticular, approximately 60 to 70% by weight based on the layersilicate are preferred when using T. ferrooxidans, T. thiooxidans or A.niger. Aqueous suspensions can also be used.

In order to control the water content when carrying out activation inthe open air, it can be necessary to guard against intensive irrigationvia rainfall (e.g. by storing under a roof, or by applying air-permeableagricultural foils) or to irrigate artificially in the case of dryweather.

The optimum duration of the activation process in individual cases isdependent on the microorganisms that are used and on the nature of thelayer silicate that is used and on the ambient conditions, and it can beascertained with ease by, the technical expert via empirical trials onthe basis of the decolorizing activity of the layer silicates that haveundergone treatment. In general, microbial activation of the layersilicate is carried out over a period of 1 to 150 days. In some cases,however, it can be advantageous to carry out microbial activation over alonger period of time, e.g. for approximately one year. The duration ofthe activation process can frequently be shortened by carrying outmechanical size reduction of the pieces of the layer silicate after e.g.one week in order to generate new surfaces for bacterial colonization.

In accordance with one form of embodiment, the process in accordancewith the invention comprises the following steps: fresh raw clay isbroken up into pieces of the order of approximately 2 cm in size; as aresult, a large surface area is generated that is accessible to themicroorganisms and the air. The clay is then mixed or kneaded with 5–20%of inoculant clay with a high concentration of bacteria and, as aresult, colonization with microorganisms is accelerated. Piles or stacksare formed that are approximately 10–50 cm high. Excessively highheaping up or compaction would prevent effective aeration. Thetemperature and water content of the clay are checked and kept asconstant as possible during microbial activation. Regular and adequatemixing together and aeration of the clay can take place, for example,via a rotary hoe every 1–8 days. The reduction of the pH value can bemeasured after drying the clay, or directly via a soil pH meter. Part ofthe activated clay is used as the inoculant clay after the desireddegree of activation has been reached (generally between pH 2 and pH 4).The remainder is dried and ground, whereby the microorganisms that arecontained in the clay are also killed off.

The use of microorganisms for the activation of layer silicates is alsothe subject of the invention.

An especially advantageous feature of the process in accordance with theinvention is that one does not have to work with corrosive acids thatcause intense burns and endanger natural water systems. Thus it issuperior to the prior art from the standpoints of operational safety andenvironmental protection. Since only very cheap raw materials, such aspyrites (which are optionally already present in the layer silicate),sulfur and water, are used for microbial activation, the process inaccordance with the invention is superior from the economic standpointas well. Thus the pyrites being a hard accompanying material do not needto be removed completely.

It has been found that the pH value or, as the case may be, the quantityof acid that is set free by the microorganisms does not correlatestrictly with the activity of the layer silicate that is to be treated.This suggests that microbial activation in accordance with the inventiondiffers from purely acidic activation, and that further metabolicproducts are involved.

Free iron ions, which are present in the activated layer silicate andwhich can interfere with the decolorization of oil, are complexed by theFe-chelating materials that are produced by the microorganisms that areused. In addition, many of the microbial organic acids complexmultivalent cations, such as Al³⁻ or Ca²⁻, and, as a result, these areremoved from the equilibrium and activation of the layer silicate.

In addition, free phosphate is incorporated into organic compounds viathe microorganisms and these organic compounds and the microorganismsadhere firmly to the layer silicate so that phosphate contamination isreduced in the oil that is to be decolorized.

In addition, interfering cations can be fixed (so-called“bio-accumulation”) via absorption into the microorganisms. Theaccumulation of Cd²⁻, Co²⁻, Cu²⁻, Cr³⁻, Fe³⁻and Ni²⁻ has beendemonstrated in the case of thio-bacteria, and the accumulation ofradionuclides, Co²⁻, Cu²⁻ and Zn²⁻ has been demonstrated in the case ofA. niger.

The surface of the mineral is also rendered more hydrophobic by themicroorganisms. The increased hydrophobicity of the surface of the layersilicate can lead to better wetting of the particles of fuller's earthby the oils that are to be decolorized.

Additional advantages can be traced back to uniform, in situ activationby the microorganisms, and to the gradual release of acids or, as thecase may be, metabolic products. Since the microorganisms that arepreferably used, such as T. ferrooxidans and T. thiooxidans, no longergrow at excessively low pH values (e.g. less than 1.5), an excessivelyhigh residual acid concentration, which is disadvantageous for thedecolorization of oils, can also be avoided in the activated layersilicate. As soon as the pH value has declined too much, themicroorganisms terminate their growth and the production of acid. Themicroorganisms thus act like an internal regulating system for theactivation of the layer silicate. Local pH peaks, which arise with easein the case of an external addition of acid, can also be avoided in thisway.

The degradation of pyrites, which is contained in the raw clay and whichis utilized by T. ferrooxidans as a nutrient substrate duringactivation, can be advantageous in some applications of the activatedlayer silicates since pyrites exhibits an abrasive action during thegrinding of the fuller's earth.

The examples of embodiments that follow below will demonstrate theinvention and the advantages relative to the prior art. However, theinvention is not limited to the examples below.

EXAMPLES Examples 1–6

Freshly mined attapulgite (palygorskite)/bentonite clay with a solidscontent of 44% was used as the starting material for comparison Examples1 and 2 and for Examples 3–6. According to x-ray phase analysis andchemical composition tests, this clay comprises 55% palygorskite, 35% Camontmorillonite, 5% quartz, 3% calcite and 1.5% pyrites. The clay wasmechanically reduced to a grain size of approximately 2 cm. This clay,which had been treated in that way, is designated raw clay A in thefollowing sections.

Example 1 (Comparison)

A sample of raw clay A was dried at 80° C. to give a water content of15% and ground to give a sieve residue (64 im) of 25%; it was then driedat 110° C. to give a water content of 8%. After suspending 8 parts ofthe sample in 100 parts of water, the pH value of the sample wasmeasured by means of a pH measurement electrode.

Decolorization experiments were carried out using rape-seed oil (100 gof oil; 0.75 g of sample; p=30 mbar; T=110° C.; t=30 minutes) and soyoil (100 g of oil; 0.50 g of sample; p=30 mbar; T=100° C.; t=30 minutes)in order to ascertain the activity of the sample for decolorizingvegetable oil. The decolorizing activity was assessed on the basis ofred values, which were ascertained by means of a Lovibond calorimeter,and on the basis of the spectrophotometrically measured chlorophyllconcentrations. In both cases, smaller values signify higherdecolorizing activity. The results are indicated in Table I(decolorization of rape-seed oil) and Table II (decolorization of soyoil); in every case, the numerical data are average values from threeexperiments.

Example 2 (Comparison)

340 g of raw clay A were intensively kneaded for 5 minutes with 50 ml ofwater and 3 g of concentrated sulfuric acid. The product was then driedand ground as in comparison Example 1. The measurement of the pH valueand that of the decolorizing activity took place as in comparisonExample 1. The results are indicated in Tables I and II.

Example 3

340 g of raw clay A were mixed with 110 ml of water and homogenized withthe help of a sterile wooden spatula. Incubation then took place in aclimatic chamber at a constant 30° C. and 100% atmospheric humidity.Homogenization of the sample was repeated once per week. Each week, asmall aliquot portion was taken out and the pH value was measured asdescribed in comparison Example 1.

When no further change in the pH value could be detected (68 days), theproduct was dried and ground as in comparison Example 1. The measurementof the pH value and that of the decolorizing activity for rape-seed oiltook place as in comparison Example 1. The results are indicated inTable I.

Example 4

340 g of raw clay A were incubated as described in Example 3. After 42days, 45 g of this material were taken out and mixed with 340 g of freshraw clay A and 110 ml of water and homogenized with the help of asterile wooden spatula. Incubation then took place in a climatic chamberat a constant 30° C. and 100% atmospheric humidity. Homogenization ofthe sample was repeated once per week. Each week, a small aliquotportion was taken and the pH value was measured as described incomparison Example 1.

When no further change in the pH value could be detected (21 days), theproduct was dried and ground as in comparison Example 1. The measurementof the pH value and that of the decolorizing activity for rape-seed oiltook place as in comparison Example 1. The results are indicated inTable I.

Example 5

1 ml of a suspension of bacteria (Thiobacillus ferrooxidans; DSMZ strain11477) and 7.0 g of pyrites (particle size<64 im) were added to 100 mlof a nutrient medium comprising 2.00 g/l of (NH₄)₂SO₄, 0.50 g/l ofK₂HPO₄, 0.50 g/l of MgSO₄.7H₂O, 0.10 g/l of KCl and 0.01 g/l ofCa(NO₃)₂, whereby this nutrient medium had been adjusted to a pH valueof 2 using sulfuric acid. A stream of air was passed through thismixture at 30° C. until the pH value of the solution had fallen to 1.75.The pyrites were separated from the solution by means of centrifugationat 1.500 g (5 minutes) and then suspended in 100 ml of water andcentrifuged again. The bacterial cells were harvested from the combinedcentrifuged liquids by centrifugation at 8,000 g (15 minutes) and thenthey were suspended in 110 ml of water.

340 g of raw clay were treated in an autoclave under standard conditions(T=120° C.; p=2 bar; t=30 minutes) in order to kill off themicroorganisms that were contained in the raw clay. The raw clay wasthen mixed with 110 ml of bacterial suspension and homogenized with thehelp of a sterile wooden spatula; incubation then took place in aclimatic chamber at a constant 30° C. and 100% atmospheric humidity.Homogenization of the sample was repeated once per week. Each week, asmall aliquot portion was taken out and the pH value was measured asdescribed in comparison Example 1. When no further change in the pHvalue could be detected (56 days), the product was dried and ground asin comparison Example 1. The measurement of the pH value and that of thedecolorizing activity for rape-seed oil took place as in comparisonExample 1. The results are indicated in Table I.

Example 6

Spores of Aspergillus niger (DSMZ strain 823) were added to 110 ml of asterile nutrient medium comprising 1.60 g/l of NH₄NO₃, 0.30 g/l ofK₂HPO₄, 0.20 g/l of MgSO₄.7H₂O, and 6.50 g of glucose, whereby thisnutrient medium had been adjusted to a pH value of 4.0 using sulfuricacid. A stream of air was passed through this mixture at 30° C. untilthe pH value of the solution had fallen to 3.0.

340 g of raw clay were treated in an autoclave under standard conditions(T=120° C.; p=2 bar; t=30 minutes) in order to kill off themicroorganisms that were contained in the raw clay. The raw clay wasthen mixed with the fungal suspension and homogenized with the help of asterile wooden spatula; incubation then took place in a climatic chamberat a constant 30° C. and 100% atmospheric humidity. Homogenization ofthe sample was repeated daily. Each week, a small aliquot portion wastaken out and the pH value was measured as described in comparisonExample 1. When no further change in the pH value could be detected (21days), the product was dried and ground as in comparison Example 1. Themeasurement of the pH value and that of the decolorizing activity forsoy oil took place as in comparison Example 1. The results are indicatedin Table II.

Examples 7–11

South American bentonite with a solids content of 60% was used as thestarting material for comparison Examples 7–9 and for Examples 10–11.According to x-ray phase analysis and chemical composition tests, thisclay comprises 90% disordered smectite/illite mixed layer minerals, 2%quartz, 2% calcite and 6% feldspar. The clay was mechanically reduced toa grain size of approximately 2 cm. This clay, which had been treated inthat way, was designated “raw clay B” in the following sections.

Example 7 (Comparison)

A sample of the raw clay B was dried at 80° C. to give a water contentof 15% and ground to give a sieve residue (64 im) of 25%; it was thendried at 100° C. to give a water content of 8%. After suspending 8 partsof the sample in 100 parts of water, the pH value of the sample wasmeasured by means of a pH measurement electrode.

Decolorization experiments were carried out using rape-seed oil (100 gof oil; 0.75 g of sample; p=30 mbar; T=110° C.; t=30 minutes) and soyoil (100 g of oil; 0.50 g of sample; p=30 mbar; T=100° C.; t=30 minutes)in order to ascertain the activity of the sample for decolorizingvegetable oil. The decolorizing activity was assessed on the basis ofred values, which were ascertained by means of a Lovibond color meter,and on the basis of the spectrophotometrically measured chlorophyllconcentrations. In both cases, smaller values signify higherdecolorizing activity. The results are indicated in Table I(decolorization of rape-seed oil) and Table II (decolorization of soyoil); in every case, the numerical data are average values from threeexperiments.

Example 8 (Comparison)

250 g of raw clay B were intensively kneaded for 5 minutes with 120 mlof water and 3 g of concentrated sulfuric acid. The product was thendried and ground as in comparison Example 7. The measurement of the pHvalue and that of the decolorizing activity for soy oil and rape-seedoil took place as in comparison Example 7. The results are indicated inTables I and II.

Example 9 (Comparison)

250 g of raw clay B were mixed with 125 ml of water and homogenized withthe help of a sterile wooden spatula. Incubation then took place in aclimatic chamber at a constant 30° C. and 100% atmospheric humidity.Homogenization of the sample was repeated once per week. Each week, asmall aliquot portion was taken out and the pH value was measured asdescribed in comparison Example 7.

After 68 days, the product was dried and ground as in comparison Example7. The measurement of the pH value and that of the decolorizing activityfor soy oil and rape-seed oil took place as in comparison Example 7. Theresults are indicated in Tables I and II.

Example 10

340 g of raw clay A were incubated as described in Example 3.

After 42 days, 46 g of this material were taken out and mixed with 250 gof raw clay B, 7 g of pyrites and 125 ml of water and homogenized withthe help of a sterile wooden spatula. Incubation then took place in aclimatic chamber at a constant 30° C. and 100% atmospheric humidity.Homogenization of the sample was repeated once per week. Each week, asmall aliquot portion was taken and the pH value was measured asdescribed in comparison Example 7.

When no further change in the pH value could be detected (42 days), theproduct was dried and ground as in comparison Example 7. The measurementof the pH value and that of the decolorizing activity for soy oil andrape-seed oil took place as in comparison Example 7. The results areindicated in Tables I and II.

Example 11

340 g of raw clay A were incubated as described in Example 3.

After 42 days, 46 g of this material were taken out and mixed with 250 gof raw clay B, 7 g of sulfur and 125 ml of water and homogenized withthe help of a sterile wooden spatula. Incubation then took place in aclimatic chamber at a constant 30° C. and 100% atmospheric humidity.Homogenization of the sample was repeated once per week. Each week, asmall aliquot portion was taken and the pH value was measured asdescribed in comparison Example 7.

When no further change in the pH value could be detected (56 days), theproduct was dried and ground as in comparison Example 7. The measurementof the pH value and that of the decolorizing activity took place as incomparison Example 7. The results are indicated in Tables I and II.

TABLE I Decolorization of rape-seed oil Red Chlorophyll Time pH value A[ppb] [d] Brief description Comparison 6.9 5.5 650 0 raw clay A example1 Comparison 2.8 4.4 300 0 raw clay A + sulfuric example 2 acid Example3 3.4 4.2 225 68 raw clay A incubated Example 4 3.4 4.1 220 21 raw clayA + inoculant clay Example 5 3.4 4.3 240 56 raw clay A inoculated withDSMZ strain Comparison 8.4 7.8 800 0 raw clay B Example 7 Comparison 2.34.6 310 0 raw clay B + sulfuric Example 8 acid Comparison 8.2 7.8 790 68raw clay B incubated Example 9 Example 10 2.6 4.2 220 42 raw clay B +pyrites + inoculant clay Example 11 2.8 4.4 290 56 raw clay B + sulfur +inoculant clay

TABLE II Decolorization of soybean oil Red Chlorophyll Time pH value A[ppb] [d] Brief description Comparison 6.9 6.4 290 0 raw clay A Example1 Comparison 2.8 6.7 180 0 raw clay A + sulfuric Example 2 acid Example6 3.4 6.0 170 21 raw clay A inoculated with A. niger Comparison 8.4 14.0680 0 raw clay B Example 7 Comparison 2.3 9.2 170 0 raw clay B +sulfuric Example 8 acid Comparison 8.2 13.8 690 68 raw clay B incubatedExample 9 Example 10 2.6 6.2 150 42 raw clay B + pyrites + inoculantclay Example 11 2.8 6.5 170 56 raw clay B + sulfur + inoculant clay

As can be seen from Table 1, it was possible to induce the naturalstrain populations of T. ferrooxidans and T. thiooxidans, which werepresent in raw clay A, to activate the layer silicate by means ofsuitable conditions. The activated fuller's earth that was obtainedexhibited good results for the decolorization of rape-seed oil andsurpassed both raw clay A (comparison Example 1) and a fuller's earth(comparison Example 2), which was prepared in accordance with the priorart by activation with concentrated sulfuric acid, in terms of the redvalues and the removal of chlorophyll.

As Example 4 shows, the duration of activation using raw clay A can bedrastically shortened by mixing it with inoculant clay, which alreadycontains large wild strain populations of T. ferrooxidans and T.thiooxidans, with equally good decolorizing activity for rape-seed oil.

A further addition of a nutrient solution to the raw clay samples inExamples 3 and 4 did not lead to increased activity of the bacteria inthe first 30 days. This can be traced back to the feature that thenatural strain populations of T. ferrooxidans and T. thiooxidans, whichwere present in raw clay A, had become adapted to very low quantities ofnutrient salt over a period of many generations.

Example 5 shows that, in addition to natural strains, cultivated strainsof T. ferrooxidans are also suitable for the activation of the layersilicate in raw clay A. The longer duration of the activation process incomparison to Example 4 can be traced back to the feature that thestrains, which have become adapted to higher nutrient saltconcentrations, first have to become adapted to the lower concentrationsin raw clay A.

As Example 6 documents, it was possible to undertake activation of thelayer silicates, which were contained in raw clay A, by means of theAspergillus niger fungus. Glucose as the nutrient source had to be addedto the raw clay in this case. It can be seen from Table II that,relative to comparison Example 1, Example 6 shows considerably betterremoval of chlorophyll and a better red value for the decolorization ofsoy oil. By contrast, treatment of raw clay A with sulfuric acid inaccordance with the prior art (comparison Example 2) results in almostequally good absorption of chlorophyll but a worsening of the red value,whereby this can be traced back to the low pH value of the adsorptionagent and to the high proportion of residual acid that is associatedtherewith.

Examples 10 and 11 show that, in addition to pyrites-containingattapulgite earths, other layer silicates are likewise capable of beingactivated via the use of microorganisms.

As far as the removal of red components and, in particular, chlorophyllis considered, comparison Example 7 shows very bad results for thedecolorization of both rape-seed oil and soy oil. According tocomparison Example 8, a distinct improvement in decolorization activityis possible via a treatment with sulfuric acid that corresponds to theprior art (see Tables I and II).

If raw clay B is merely incubated (comparison Example 9), then noimprovement in decolorizing activity occurs. This can be traced back tothe deficiency in energy-supplying accompanying substances (such as e.g.pyrites) in raw clay B and the absence, which is related thereto, ofmicroorganisms (e.g. T. ferrooxidans) that utilize these accompanyingsubstances.

Example 10 shows that activation of the layer silicate in raw clay B canbe achieved by an addition of pyrites as the supplier of energy togetherwith inoculant populations of T. ferrooxidans and T. thiooxidans fromraw clay A and subsequent incubation. In comparison to raw clay B(comparison Example 7) and raw clay B that had been activated inaccordance with the prior art (comparison Example 8), a distinctimprovement in decolorizing action is found both in rape-seed oil (TableI) and in soy oil (Table II). The duration of the activation process hasbeen prolonged relative to Example 4. It is probable that the bacteria,which have become adapted to the conditions in raw clay A, first have tobecome adapted to the ambient conditions that prevail in raw clay B.

It can be seen from Example 11, that activation of the layer silicate inraw clay B can also occur by supplying elemental sulfur, followed byinoculation with incubated raw clay A and subsequent incubation. Theduration of activation is further prolonged relative to Example 10because the wild strain populations of T. thiooxidans from raw clay Ahave to become adapted not only to the changed conditions in raw clay B,but also to the non-adapted energy source. Relative to comparisonExamples 7 and 8, the layer silicate that was activated in accordancewith Example 11 exhibits improved activity levels for decolorizingrape-seed oil and soy oil. In comparison to Example 10, lowerdecolorizing activity was found in the two oils that were investigated;in contrast to this. Example 11 offers the possibility of activationwithout the addition of pyrites.

1. A process for increasing the decolorizing activity of a layersilicate for treatment of oils, fats and waxes comprising steps oftreating without the addition of an acid, other than the acid producedby an acid-producing microorganism, the layer silicate, by the additionof acid-producing microorganism until a pH value of the layer silicatebetween 2 and 4 is obtained, thereby activating the layer silicate, andmeasuring the decolorizing activity of the activated layer silicate. 2.The process of claim 1 wherein the layer silicate comprises a smectiteclay.
 3. The process of claim 1 wherein the layer silicate comprises amontmorillonite clay.
 4. The process of claim 3 wherein themontmorillonite clay comprises a bentonite clay.
 5. The process of claim1 wherein the layer silicate comprises a palygorskite clay.
 6. Theprocess of claim 4 wherein the layer silicate further comprises apalygorskite clay.
 7. The process of claim 1 wherein the acid-producingmicroorganism comprises a sulfur-oxidizing bacteria.
 8. The process ofclaim 1 wherein the acid-producing microorganism comprises aniron-oxidizing bacteria.
 9. The process of claim 7 wherein thesulfur-oxidizing bacteria comprises Thiobacillus thiooxidans.
 10. Theprocess of claim 8 wherein the iron-oxidizing bacteria comprisesThiobacillus ferrooxidans.
 11. The process of claim 1 wherein theacid-producing microorganism produces citric acid.
 12. The process ofclaim 11 wherein the citric acid-producing microorganism comprisesAspergillus niger.
 13. The process of claim 1 wherein the layer silicateis in the form of raw clay and wherein the process further comprisesbreaking up the raw clay into clumps with a size from about 0.5 cm toabout 5 cm prior to treating the layer silicate.
 14. The process ofclaim 1 further comprising adding the acid-producing microorganisms toan inoculant material prior to treating the layer silicate with themicroorganisms which have been added to the inoculant material.
 15. Theprocess of claim 14 wherein the population of the microorganisms addedto the layer silicate is from about 10² to about 10¹⁰ bacteria/g of theinoculant material.
 16. The process of claim 1 further comprisingmaintaining the temperature of the layer silicate during treating withinthe range from about 20 to about 35° C.
 17. The process of claim 1further comprising maintaining the water content of the layer silicateduring treating within a range from about 15 percent by weight to about70 percent by weight.
 18. The process of claim 14 wherein the inoculantmaterial added to the layer silicate comprises about 5 to about 20percent of the overall composition after the inoculant material has beenadded.
 19. The process of claim 1 further comprising mixing and aeratingthe layer silicate while it is being treated with the acid-producingmicroorganism.
 20. The process of claim 19 wherein the treating processoccurs for a period of time from about 1 to about 365 days.
 21. Theprocess of claim 1 further comprising adding nutrients for themicroorganisms to the layer silicate prior to treating with theacid-producing microorganisms.
 22. The process of claim 21 wherein thenutrients added comprise sulfur-containing products.
 23. The process ofclaim 1 wherein the pH level is determined by suspending 8 parts of asample of the treated layer silicate in 100 parts of water and measuringthe pH-value by means of a pH measurement electrode.